1. Field of the Invention
The present invention relates to a knee prosthesis and more specifically to the device for assembling its tibia plate, which is made of plastic, on its metal base anchored beforehand into the tibia bone tissue.
2. Discussion of the Background Information
Knee prostheses which comprise a plastic tibia part which is free to rotate about the tibia bone axis with respect to the metal base secured to the tibia are known.
This freedom of rotation is generally achieved via a male shaft integral with the plastic tibia part which engages with a bore made in the metal base.
Furthermore, this freedom of rotation may be achieved by a male shaft secured to the metal base which engages with a bore made in the plastic tibia part.
These connecting devices have certain drawbacks, namely the difficulty of inserting the plastic tibia plate once the metal base is in place on the tibia. These drawbacks are exacerbated when the posterior cruciate ligament is being kept, as this restricts access to the upper part of the tibia.
Furthermore, it is observed that the center of rotation is necessarily positioned at a point of the device or [sic] the bore can be made, that is to say in a part or [sic] there is enough material to make the said bore. This arrangement of the center of rotation is not strictly anatomical.
It can be seen that the volume generated by the tibia bone axis may prevent a posterior cutout from being made in the plastic tibia plate or in the metal base to allow the posterior cruciate ligament to be kept.
Knee prostheses which comprise a plastic tibia plate which slides freely over the flat surface of the metal base, and the movement of which is limited by one or more cylindrical studs integral with the base communicating with spaces made in the plastic plate are also known.
This type of prosthesis has the drawback of not physically embodying an axis of rotation.
It is these drawbacks which the present invention sets out more particularly to overcome.